1. Field of the Invention
The present invention relates to a signal processing apparatus and method, a recording apparatus, a playback apparatus, and a recording and playback apparatus, which are capable of most effectively performing decoding by data which can be played back even if there is a loss of video data which is played back from a recording medium when video data which is compressed and coded, and recorded by using DCT (Discrete Cosine Transform) is played back at variable speed.
2. Description of the Related Art
In recent years, several formats used for recording digital video signals in a recording medium and for transmitting digital video signals by using a network have been provided. Generally, since digital video signals require a very large amount of data, when these signals are to be recorded in a recording medium for a long time, it is necessary to compress and code them. As a typical compression coding method, an MPEG (Moving Picture Experts Group) method is known.
The MPEG method is a compression coding method of a hybrid method in which motion compensation predicative coding and coding by DCT (Discrete Cosine Transform) are combined. That is, initially, redundancy in the direction of the time axis is reduced by calculating a difference among frames of a video signal. Next, redundancy in the direction of the space axis is reduced by using DCT. These make it possible to perform efficient coding.
In the MPEG method, one screen is divided into macro blocks composed of, for example, 16 pixelsxc3x9716 lines, and the macro block is further divided into DCT blocks composed of, for example, 8 pixelsxc3x978 lines. For example, when the format of a video signal conforms to the NTSC method, in accordance with the ratio of each signal component, four DCT blocks of a luminance signal Y and two DCT blocks each of color signals Cr and Cb are formed. DCT is performed in units of these DCT blocks. Then, the DCT coefficient obtained by DCT is arranged from the DC components and the low-frequency components to the high frequencies components for each DCT block by zigzag scan, and this is performed on each of the DCT blocks which constitute a macro block.
In the meantime, as a recording medium for recording video signals, a magnetic tape is commonly used. Recording of video signals onto a magnetic tape is performed in such a way that what are commonly called xe2x80x9chelical tracksxe2x80x9d, which are inclined obliquely to the direction of tape movement, are formed by a magnetic head (rotary head) provided on a rotating drum. During playback, helical tracks formed during recording are accurately traced by the rotary head.
By making the tape movement speed during playback, higher than that during recording, for example, playback of 2x speed, 3x speed, or search can be performed. In this case, the trace angle of the rotary head on the tape becomes different from the inclination axis of the helical tracks. For this reason, it is not possible to trace all the signals recorded on the helical tracks. That is, during high-speed playback, playback is performed in which a part of each helical track is scanned, for example.
In a case in which compression coding is performed using MPEG and the data is recorded on a tape-like recording medium, when high-speed playback, such as the above-mentioned search, is performed, only a part of each helical track is traced. For this reason, for example, in a case in which the data of the second half in the above-mentioned macro block cannot be obtained, only DCT blocks of parts corresponding to the first half of the macro block can be used, causing a considerable decrease in image quality. In this manner, conventionally, there is a problem in that it is difficult to effectively use played-back data in order to obtain a high-quality playback image.
Accordingly, an object of the present invention is to provide a signal processing apparatus and method, a recording apparatus, a playback apparatus, and a recording and playback apparatus, which are capable of obtaining a high-quality image even if high-speed playback is performed during playback when a magnetic tape in which data is recorded on helical tracks by performing compression coding using MPEG is played back.
To achieve the above-mentioned object, according to a first aspect of the present invention, there is provided a signal processing apparatus for dividing each frame contained in video data into a plurality of macro blocks and for performing DCT on each of a plurality of DCT blocks contained in each divided macro block in order to create DCT coefficient data, the signal processing apparatus comprising conversion means for rearranging the arrangement of DCT coefficient data which is coded independently for each DCT block into the sequence from the low-order coefficient data having a low spatial frequency to the high-order coefficient data having a high spatial frequency in such a manner as to extend across a plurality of the DCT blocks within a macro block.
According to a second aspect of the present invention, there is provided a signal processing apparatus for processing DCT coefficient data which is created in such a way that each frame contained in video data is divided into a plurality of macro blocks and DCT is performed on each of a plurality of DCT blocks contained in each divided macro block, the signal processing apparatus comprising conversion means for rearranging the arrangement of the DCT coefficient data arranged in the sequence from low-order DCT coefficient data into the coefficient data of a high order in such a manner as to extend across a plurality of DCT blocks within a macro block into the sequence from the low-order coefficient data to the high-order coefficient data independently for each of the DCT blocks.
According to a third aspect of the present invention, there is provided a signal processing method for dividing each frame contained in video data into a plurality of macro blocks and for performing DCT on each of a plurality of DCT blocks contained in each macro block in order to create DCT coefficient data, the signal processing method comprising: a conversion step for rearranging the arrangement of DCT coefficient data which is coded independently for each DCT block into the sequence from the coefficient data of a low order to the coefficient data of a high order in such a manner as to extend across a plurality of the DCT blocks within a macro block.
According to a fourth aspect of the present invention, there is provided a signal processing method for processing DCT coefficient data which is created in such a way that each frame contained in video data is divided into a plurality of macro blocks and DCT is performed on each of a plurality of DCT blocks contained in each divided macro block, the signal processing method comprising: a conversion step for rearranging independently for each of the DCT blocks, the arrangement of the DCT coefficient data arranged in the sequence from low-order DCT coefficient data into the coefficient data of a high order in such a manner as to extend across a plurality of DCT blocks within a macro block into the sequence from the low-order coefficient data to the high-order coefficient data.
According to a fifth aspect of the present invention, there is provided a recording apparatus for recording DCT coefficient data which is created in such a way that each frame contained in video data is divided into a plurality of macro blocks and DCT is performed on each of a plurality of DCT blocks contained in each divided macro block, the recording apparatus comprising: conversion means for rearranging the arrangement of DCT coefficient data which is coded independently for each DCT block into the sequence from the coefficient data of a low order to the coefficient data of a high order in such a manner as to extend across a plurality of the DCT blocks within a macro block; packing means for performing packing by assigning the coefficient data rearranged by the conversion means to a fixed-length frame for each of the macro blocks and for packing in sequence the portion which extends outside the fixed-length frame into a portion which is unfilled in the fixed-length frame; error-correction coding means for performing error-correction coding using a product code on data which is packed by the packing means and which corresponds to a plurality of the fixed-length frames; and recording means for recording data which is error-correction-coded by the error-correction coding means in a recording medium.
According to a sixth aspect of the present invention, there is provided a playback apparatus for playing back data recorded in a recording medium in such a way that each frame contained in video data is divided into a plurality of macro blocks, DCT is performed on each of a plurality of DCT blocks contained in each divided macro block in order to create DCT coefficient data, the DCT coefficient data is rearranged in the sequence from low-order DCT coefficient data to high-order DCT coefficient data in such a manner as to extend across a plurality of DCT blocks within a macro block, the rearranged DCT coefficient data is assigned to a fixed-length frame for each macro block, the portion which extends outside the fixed-length frame is packed in sequence into a portion which is unfilled in the fixed-length frame, and error-correction coding using a product code is performed on packed data corresponding to a plurality of fixed-length frames, the playback apparatus comprising: playback means for playing back data recorded in a recording medium; error-correction means for performing error correction by decoding an error-correction code using a product code of the data played back by the playback means; depacking means for reconstructing a macro block by concatenating corresponding macro blocks with respect to data on which error correction is performed by the error-correction means; and conversion means for rearranging independently for each of the DCT blocks, the arrangement of the DCT coefficients arranged in the sequence from low-order DCT coefficients to the high-order coefficients in such a manner as to extend across a plurality of DCT blocks within a macro block reconstructed by the depacking means into the sequence from the low-order coefficients to the high-order coefficients.
According to a seventh aspect of the present invention, there is provided a recording and playback apparatus which records, in a recording medium, DCT coefficient data which is created in such a way that each frame contained in video data is divided into a plurality of macro blocks and DCT is performed at intervals of a plurality of DCT blocks contained in each divided macro block in order to create DCT coefficient data, and which plays back DCT coefficients from the recording medium, the recording and playback apparatus comprising: first conversion means for rearranging the arrangement of DCT coefficient data which is coded independently for each DCT block into the sequence from the coefficient data of a low order to the coefficient data of a high order in such a manner as to extend across a plurality of the DCT blocks within a macro block; packing means for performing packing by assigning the coefficient data rearranged by the conversion means to a fixed-length frame for each of the macro blocks and for packing in sequence the portion which extends outside the fixed-length frame into a portion which is unfilled in the fixed-length frame; error-correction coding means for performing error-correction coding using a product code on data which is packed by the packing means and which corresponds to a plurality of the fixed-length frames; recording means for recording data which is error-correction-coded by the error-correction coding means in a recording medium; playback means for playing back data recorded in the recording medium; error-correction means for performing error correction by decoding an error-correction code using a product code of the data played back by the playback means; depacking means for reconstructing a macro block by concatenating corresponding macro blocks with respect to data on which error correction is performed by the error-correction means; and second conversion means for rearranging independently for each of the DCT block, the arrangement of the DCT coefficients arranged in the sequence from low-order DCT coefficients to the coefficients of a high order in such a manner as to extend across a plurality of DCT blocks within a macro block reconstructed by the depacking means into the sequence from the low-order coefficients to the high-order coefficients.
In a manner as described above, the signal processing apparatus and method, the recording apparatus, and the recording and playback apparatus in accordance with the present invention rearrange the arrangement of DCT coefficients which are coded independently for each DCT block into the sequence from low-order coefficients to high-order coefficients in such a manner as to extend across a plurality of DCT blocks. This makes it possible to use data starting from a low order for each of a plurality of DCT blocks even if all data of the plurality of DCT blocks within a macro block cannot be played back during playback.
In addition, in a manner as described above, the signal processing apparatus and method, the playback apparatus, and the recording and playback apparatus in accordance with the present invention rearrange independently for each DCT block, the arrangement of DCT coefficients arranged in the sequence from low-order DCT coefficients to high-order coefficients into the sequence from low-order coefficients to high-order coefficients in such a manner as to extend across a plurality of DCT blocks within a macro block. This makes it possible to use data starting from a low order for each of a plurality of DCT blocks even if all data of the plurality of DCT blocks within a macro block cannot be played back during playback.